The present invention relates to a method for mounting electronic components and structures having mounted thereon electronic components, and more particularly, the invention relates to a method for mounting electronic components and structures having mounted thereon electronic components in which electrodes of the electronic components are mounted by connecting the electrodes to wiring electrodes of substrates via bumps.
FIG. 7 shows an example of a structure where an electronic component is mounted on a substrate (a substrate used for mounting) via bumps by a conventional method. In such a structure, the top portions of Au bumps (protruding bumps) 53 are on surfaces of electrodes 52. The bumps 53 disposed on electrodes 52 are formed on a surface of an electronic component 51. The bumps 53 are connected to wiring electrodes (substrate pads) 55 of a substrate 54 by a conductive adhesive (a conductive paste) 56. An insulating bonding resin 57 fills a gap between the electronic component 51 and the substrate 54, and mounts the electronic component 51 on the substrate 54.
In the above-described method for mounting the electronic component, the conductive adhesive 56 (the conductive paste) is applied at the top portions of the Au bumps (the protruding bumps) 53 formed on the electronic component 51 through wire bonding technology. The insulating bonding resin 57 is applied to the wiring electrode 55 of the substrate 54. Then, the conductive paste 56 is temporarily hardened. After this, while pressing the electronic component 51 on the substrate 54, heat is applied to connect the Au bumps 53 of the electronic component 51 and the wiring electrodes 55 of the substrate 54, which hardens the conductive adhesive (the conductive paste) 56 and the bonding resin 57 to mount the electronic component.
In the above-described method for mounting an electronic component, there are some problems:
(1) A material (a conductive paste) whose conductive component (filler) is formed of Ag or an alloy of Ag is typically used as the conductive adhesive, which leads to an increase in cost;
(2) although the bonding resin is used to enhance the bonding strength, since bonding only by applying small amounts of conductive adhesives at the top portions of the Au bumps is not strong enough, there is insufficient strength, and no moisture resistance; and
(3) when the electronic component is mounted by pressing on the substrate and hardening the conductive adhesive (the conductive paste) and the bonding resin, since the Au bumps formed by using wire bonding have protruding configurations, the substrate, (which is typically formed of resin), flush against the lower side of the wiring electrode, is deformed. The deformation affects the connection reliability, and particularly, the moisture resistance.
Accordingly, the present invention is aimed at solving the above-described problems. It is an object of the present invention to provide a highly reliable method for mounting an electronic component and structure having mounted thereon an electronic component, in which the electronic component can be efficiently mounted on a substrate without expending significant cost.
To this end, according to one aspect of the present invention, there is provided a method for mounting an electronic component by connecting an electrode of the electronic component to a wiring electrode on the substrate via a bump, the method including the steps of:
disposing the top portion of an ultrasonic-wave applying unit (a collet) flush against the electronic component;
positioning the electronic component on the wiring electrode of the substrate, which is heated, via the bump,
applying ultrasonic oscillation to the electronic component under a condition in which the oscillating amplitude of the top portion of the collet is larger than the oscillating amplitude of the electronic component, where the oscillating amplitude of the electronic component is 0.20 xcexcm or larger, and
metallically bonding the bump, and the electrode of the electronic component or the wiring electrode on the substrate, which are objects to be connected, so as to mount the electronic component on the substrate via the bump.
In this case, while disposing the top portion of the collet flush against the electronic component and positioning the electronic component on the wiring electrode of the substrate, which is heated, via the bump, the ultrasonic oscillation is applied to the electronic component under the condition in which the oscillating amplitude at the top portion of the collet is larger than the oscillating amplitude of the electronic component, where the oscillating amplitude of the electronic component is 0.20 xcexcm or larger. As a result, without using an expensive conductive adhesive (a conductive paste), the bump, and the electrode of the electronic component or the wiring electrode on the substrate, which are objects to be connected, can be metallically bonded to reliably connect the bump and the electrode of the electronic component or the wiring electrode on the substrate.
In other words, with frictional heat caused by the ultrasonic oscillation, where the oscillating amplitude of the top portion of the collet is larger than the oscillating amplitude of the electronic component, and heat provided by heating, it is possible to produce a sufficient atomic diffusion between the bump and the electrode of the electronic component or the wiring electrode on the substrate. As a result, it is possible to obtain a sufficiently reliable connection, and moisture resistance, by metallically bonding the bump and the electrode of the electronic component or the wiring electrode on the substrate.
In addition, in the method for mounting an electronic component in accordance with the present invention, since the bump and the electrodes are metallically bonded while applying ultrasonic oscillation, it is possible to provide the heat energy necessary to perform metallic bonding at relatively low temperatures to avoid deforming the substrate. Accordingly, the deformation of a substrate, which occurs in a conventional mounting method, can be suppressed or prevented.
Furthermore, in the method for mounting an electronic component in accordance with another aspect of the invention, the bump is formed by plating and is made of a material including gold (Au) as a main component.
Although the present invention can also be applied in the cases of bumps formed by various methods and formed of various materials, when a plated bump flatly formed on a surface of an electrode is used, it is generally possible to suppress deformation of the substrate that occurs in the case of a bump with a protruding configuration. Thus, this is advantageous in improving characteristics such as moisture resistance. At the same time, the bonding strength can be improved since a large area for bonding can be provided. In addition, in the case of the bump plated by the material including gold (Au) as the main component, it is possible to metallically bond the bump to the electrode of the electronic component or the wiring electrode of the substrate by heating while applying the ultrasonic oscillation, with the result that the electrode of the electronic component can be reliably connected to the wiring electrode of the substrate via the bump.
Furthermore, in the method for mounting an electronic component in accordance with another aspect of the invention, the thickness of the substrate is 0.2 mm or less.
When the thickness of the substrate is increased, the substrate absorbs the ultrasonic oscillation. As a result sufficient frictional heat cannot be generated between the bump and the electrode of the electronic component or the wiring electrode of the substrate. However, when the thickness of the substrate is 0.2 mm or less, the substrate can be prevented from absorbing the ultrasonic oscillation so that sufficient frictional heat can be generated between the bump and the electrodes.
Furthermore, in the method for mounting an electronic component in accordance with another aspect of the invention, after connecting the electrode of the electronic component and the wiring electrode of the substrate via the bump, the overall electronic component is covered and sealed with a resin.
After connecting the electrode of the electronic component and the wiring electrode of the substrate via the bump, the electronic component itself and the overall electronic component are sealed by covering. With this arrangement, further improvement in weather resistance and moisture resistance can be achieved so as to enhance reliability.
Furthermore, in the method for mounting an electronic component in accordance with another aspect of the invention, after connecting the electrode of the electronic component and the wiring electrode of the substrate via the bump, a bonding resin for bonding the electronic component and the substrate fills a gap between the electronic component and the substrate. In addition, the overall electronic component is covered and sealed with a sealing resin.
When the bonding resin for bonding the electronic component and the substrate fills the gap between the electronic component and the substrate, and then the overall region including the electronic component and the part where the electronic component and the wiring electrode on the substrate are bonded is sealed by covering, both the bonding force due to the metallic bonding between the bump and the electrodes and the bonding force of the bonding resin further improve the reliability of the connection. This enhances moisture resistance and weather resistance, and significantly improves reliability.
In addition, according to the present invention, there is provided a structure having mounted thereon an electronic component, in which the electronic component is mounted by the method in accordance with the method discussed above. In this structure, an electrode of the electronic component is electrically and mechanically connected to a wiring electrode of a substrate by a bump, a bonding resin fills a gap between the electronic component and the substrate, and the overall electronic component is covered with a sealing resin.